Transistor voltage regulator



Aug. 20, 1963 A. A. CURRY TRANSISTQR VOLTAGE REGULATOR Filed Aug. 4, 1958 INVENTOR. ARNET A. CURRY By M #M Where a protective elenien TRANSISTOR VOLTAGE REGULATOR Arnet A. Curry, Elmhurst, lll.,'assig'nor to Motorola, Inc.,

Chicago, IlL, a corporation oflllinois Filed Aug. 4, 158,Ser. No. 752,899 r r '5 Claims. (CL 323-22) This. invention relates to voltage regulator and more particularly to a transistor voltage regulator in cooperating means tor protecting a control transistor of such a system from overloading under abnormal op el at ing conditions. There are numerous applicationsin which it is desirable to provide a relatively constant direct current output voltage regulated against variations "in input voltage and against changes in load. One system for such use. em-

= States Patent" ploys a control tnansistorconnected so that its biasf voltage is controlled by the diiference betweenaa constant reference voltage and the output voltage. 1 Changes in output voltage thus produce a biasing jsignal varying the conductivity of the transistor. Such conductivity varia- Patented Aug. 20, 1963 o I 2 [from being thrown into conduction under conditions which might damage it.

A further feature of the invention is the provision of a switching transistor'having a pair of resistors connected serially between its base and emitter and with the voltage derived across such resistors, which controls conduction of the transistor, being'responsive to changes in output current and voltage. 'The' polarity of the voltage vectors derived across the resistors are opposingfso that their algebraic sum becomes suificient to cause conduction to take place instantly when the output voltage drops and jthe ou-tput current rises at the same time, and upontermination of this condition, the voltage applied to the switching transistor immediately drops to a value rendering it non-conductive and rea'ctivating the regulator portion of the system. 1

- The accompanying single FIGURE of drawings is a circuit diagram of a transistor. voltage regulator embodying 1 the protective featuresdot the present invention. A

- In accordance "with the invention, a direct current voltage regulator includes control means such as a transistor tion isused in various ways to restore the-output voltage to its predetermined value. Ui der abnormal operating conditions, such as those produced by a total or partial short circuit across the load, the temporary drop in out- 1 put voltage and the corresponding increase in voltage drop across the regulator is quite substantial. The decrease v in output voltage is accompanied by a corresponding 7 increase in output current the result that there is a corresponding increase in the conductivity of the tram sistor andinthe amount of power it-rnust dissipate. .In

many: instances, the power increase is so large itmlay cause the transistor to become. overheated and break down resulting in failure of the regulator system.

'llle use of conventional protective-devices, such-.ias

having its base coupled to a reference voltage element and having. its emitter and collector connected across a resistor in "in the line to be regulated. A second transistor. is connectedto one side of the reference voltage element and is connectedin circuit so that its base to emitter,. =bias voltage is the algebraic sum of signal voltages otqopposite polarity, one of which reflects output voltage of thesystem and the other of which reflect-s its output current; When the outputcurrentnises and the outputvoltag'e'rlrdps s multaneously, as when there is "a partial-short circuit across the load of system, the

thenr'nally operated switcheafof this purpose has not been entirely satisfactory since such "means are generally too slow acting to be effective. Conventional protective de vices are also. generally incapable'uofdistinguishing be- ,tweenyabnorm'al 'cohditions,fsnch as short circuits, and:

taneou sly .efiective protective features .to lprevent over loadingorf a control element subject to brealgdown.

It is a further object of the invention to provide a transistor voltage regulator system which protects the control transistor-rag inst overloading or thetype caused by short circuits across the ontput terminals. i I

It is anotherpbjectof the invention to provide a tram sister voltage regulator eifective to. discriminate between temporary abnormal operating "conditions such as short circuitsand other changes in operating conditions which the system is capable of regulating without danger of destruction of the control transistor; f

A feature ofthe present invention isthe provision of ment isbypassed upon the loccurrenceof ashort circuit across the load of thesystem. 5 3

Another feature of the invention is the oornbinationot a sv'litching transistor coupled to :one side of; a reference switching-transistor is thrown into conduction thus eifectively unclainpingi the side of the reference voltage eleinent to which itis connected in common with'the base of thetirst transistor and decreasing-the reference voltager? Since "the control. transistor becomes conductive only lin response to a diifierence signal between the output voltage and the reference voltage, simultaneous dei creasein these twovoltages prevents the difference signal from becoming large enough to throw the control tnan sistor into conduction. .Inthis way, thecontrol transistor is protectedtrom being thrown into conduction under 'abnonm'al andpotentially destructive operating conditions a The series vbltagefi egulator system illustrated includes input terminals name .12 connected to an unregulated a device sensitive to simultaneous changes in output volt-, age and output current so thatia voltage regulating elevol-tageelement of a voltage regulator and connected to i become conductive upon a simultaneous increase in out= putcurrent and decrease in output voltage'lto the end that the reference voltage, supplied is decreased and the a voltage, regulating transistor ofthe system is prevented 1 vent-ion, provided-they serve 'D.C. voltageh source and output terminals 13 and 14 acros s which a load indicated by the resistor 16 is con- Iiected. The. control section of the system includes the p-np t-ransistor' 17 having base 18,"'collector 19, and

Y emitter 21ffThe emitter-collector circuit of the control transistor is connected across the series resistor 22.

voltage. reference section includes the voltage reference element 23 iand the resistor 24 connected in series-across the inputterminals L1 and 12; The reference element 23l is shown as a Zener diode which is a convient ,and effective component forproviding a constant reference voltage. It will be understood, however, that other reference. voltage elements, such esba'tteries, may be suhstitutedftherefor in some embodiments of the inthe function of providing a constant voltage drop. V I The Zener idiode 23 is effective. to clamp the point 26 at a constant potential and the base 18 of the transistor 17 is connected to this point; This controls the conductivity' between the collector 19 and'ernitter 21 to provide regulating actionlas will be further described. The protective portion of the system is made up of the switching transistor 27 which is illustrated as a p-n-p unit. 'I he'polarity of the output voltage may be reversed f fronithat shown,- if desired, by substituting n-p-n units attain I for the tjra nsistors 17 and H 27. The transistor 27 may be the same type of transistor as the control or regulating unit and both are typically alloyed junction devices.

' Transistor 27 includes haste -28 collector 29,. andemitter 31. Emitter '31 is connected between the resistors 32 and 33 which form a voltage divider across theiloutput I terminals of the system. A resistor 340i relatively'low ohmic value is connected in series with resistor 33 between base 28 and emitter '31 of. the switchin'gft'ransistor.

During normal conditions of operation, the point 36 v to which the emitter 31 isconnected is substantiallyrnore is to establish direct connection between collector 29 and input terminal 11 through dropping resistor 24 and the -point 26. This effectively iinclamps the point 26 and negative than the point 37 to which the base .28 iscou;

pied. This results inreverse biasing. of the emitter-base junction of the transistor 27 so that the'unit is non con ductive and effectively out of the circuit. Under these conditions, the voltage drop, designated as E across the Zener diode 23 is a constant value so that the point26 is clamped ata fixed. potential; The base 'to emitter biasvoltage of the regulator control transistor17 is thus equal to the difference between the reference/voltage E and reduces the voltage drop across Zener diode 2'3 substantially to Zero. For this reason, E4 cannot be greater than E so that there is no difference signal to turnpon transistor 17 and it thusremains non-conductive and is protected from overloading. I

Upon termination of the short circuit condition, the transistor 27Iis immediately rendered non-conductive to re-establish the reference voltage drop across Zener diode 23' and reactivate the, regulatory section of the system so that transistor 17 isagainefi'ect-ive to regulate the output the output voltage E When E drops below .Eothe resultant .diflerence signal applies a bias whicheffectivelydecreases the collector to emitter resistivity'of transistor L7. This causesless current. applied atfinp'ut' tfe'rinina l ll to flow through the shunt resistor 22 thus ldecreasin'gthei voltage drop E acrossthe shunt resistor and tending to restore the output voltage E 'to it's regulated value, Le.

the reference voltage E4. The value of resistor is I chosen so thatv the maximum input voltage available will be. dropped to the desired output value under conditions of anticipated minimum current drawn through the load.

Operation of the system under normal conditions wherein the input voltage and/or load vary is well known and will not be idescribed'in. further detail'." f p I Under abnormal conditions of operation, such as; occur when there is a total or partial sh'ort circuit'across the output load 16, the output. voltage E will drop to a very low value, so that the difierencefvoltage E -E applied acrosst-he base-emitter connection of transistor I7 is'quite large. There-is a correspondingincrease in the current I t-hrough'the control transistor 17 due to its; sharp increase in conductivity, At the sarnejtime,

voltage.

It will be noted that the effect required to'turn on transistor 27 is a differential one caused by a decrease in output voltage and a simultaneous increase in output curj rent. Under normal conditions of operation, a drop in output voltage such as is caused by a change in'the value Thie circuit.components employed had the following values;

Resistor 22n 12.5 ohms. I I Zender diode 2=3 TypevHZPR-56 (60 volt drop); Transistors 1 7' and 2,7 2N-618'. Resistor 24 1000 ohms.

voltage drop E increases since E is equal to the' input ena e E minus the output voltage E The poWerdis-' sipation in. transistor,17 is equal to" the product "of E and 1 so. thatan increase inb'oth these quantities simulg taneously produces a veryfIsubst-antial amount of heat'. In many instances, this heat cannot be dissipated ader quately .so that itiraises the temperature of the. transistor '17 to the extent that breakdown taltes place and the sys-.-

tem becomes inoperative.

The present invention solves to. regulating transistors under such conditions by means of the protective circuit including the switching transistor 27'. Thistransistoris connected so as to effectively sample both the output voltage E and the output current 1 ofv the system. When a short circuit oocursin the load 16, the voltage drop across resistor 35; decreases in proportion to the. drop in output vohage. At the same time, the. voltage drop across resistor 34 increases due to the increase in .output current '1 flowing therethrough; The voltage drops developed across resistors 33 and ,34

are of opposite polarity (as indicated by the voltage vector arrows) and,. since they are. connected-between basexZS and emitter 31, the bias voltage cont-Trolling the conductivity of switching transistor 27 isincreased, being the algebraic sum of the, two developed yoltages. In other words, the point 36 to whi'ch emitterjiil isconnected becomes. less negative while the point 37 to which the. base 28 connected becomes more negative. At the point where the;..lbase connection is.,negative with respect to the emitter connection, the transistor 27.- is

I turned on.- In -present day-"transistorsthisactiongis suhstantially'instantaneousr. o o a The: effect: oithro'wing'v transistor 27 into conduction the problem: of damage Additional transistorsniay, of course, be connected in parallel. withtransistor \17 to increase the current range of the regulator circuit. Irrsomecommercial embodi-' merit-sot this circuit two regulator transistors are used. f I The present invention'proyides an efiectivejprotective circuit to prevent the self-destruction of voltage regulating elements, such as transistors, which maybe damaged by over-loading. At the same time, the operation of the switching transistor due to a diiferentialaction enable the system to discriminate between abnormal conditions of operation, such as short circuits, and normal regulation requirements; a

fclaimz A direct current voltage regulator includingv in combination, input supply terminals, output'terminalsfor connection to a load, a control'transistor connected be-Q tween said input and said output terminals,;a Zener diode for supplying a reference voltage, said control transistor being coupled to said Zener diode and operative to apply currentto one of saidoutput terminals substantially to eliminate changes in voltage across the load in response to a detected difference between the output voltage and the reference voltage supplied by the voltage drop across .saidhZ'ener diode, a switching transistor having base, emitter and collector electrodes, said collector electrode being coupled to one side of said Zener diode, and first and second resistors connected in series between said base v and emltter electrodes of said switching transistor and producing a resultant voltage to normally bias off said switching transistor, said first resistor being coupled across said output terminals and having a first voltage-developed thereacross which varies directlyvwith the output voltage, said second resistor being coupled to one of} said output terini'nalsand having a second voltage developed thereacross This' perr'nitsthe regulating transistor 17 to.

which varies directly with the output current applied to the load, said second voltage being of opposite polarity to said first voltage and exceeding said first voltage upon the occurrence of a simultaneous decrease in output voltage and increase in output current to provide a resultant bias voltage which renders said switching transistor conducting, said switching transistor reducing the voltage across said Zener diode to cut off said control transistor.

2. A direct current voltage regulator including in com- I bination, first and second input supply terminals, first and second output terminals for connection to a load, regulating means coupling said first input supply terminal and said first output terminal, said regulating means including a control transistor having base, emitter and collector electrodes, means connecting said emitter electrode to said first output terminal and connecting said collector electrode to said first input supply terminal, means providing a substantially constant reference voltage between said base electrode and said second output terminal, said control transistor responding to oppose any changes between load voltage and said reference voltage, and protection means to disable said control transistor to protect the same from the harmful eifects of short circuits occurring in the load, said protection means including asecond transistor having base, collector and emitter electrodes, and first and second bias elements, said collector'el-ectrode of said second transistor being coupled to said base electrode of said control transistor, said first and second bias elements being serially connected between said base and emitter electrodes of said second transistor and providing a resultant bias voltage therebetween, said first element being coupled to said output terminals and being responsive to the output voltage thereat to produce a first voltage component which decreases in response to a short circuit condition in the load, said second element'being coupled to at least one of said output terminals and being responsive to the output current applied to the load to produce a second voltage component which increases in response to short circuit conditionsappearing in the load, said first and second voltage components being of opposite polarities and combining in series to provide a resulting bias voltage, said first component opposing said second component to provide a normal resultant bias voltage such that said second transistor is non-conducting, said second component exceeding said first component in the event of a short circuit in the load to provide aresultant bias voltage which renders said second transistor conducting to disable said regulating means.

3. A voltage regulator system including in combina-.

tion, first and second input supply terminals, first and second output-terminals for connection to a load, regulating means coupling said first input supply terminal and said first output terminal, a reference device providing a substantially constant reference voltage, said regulating means including means to substantially counteract cletected changes between the load voltageat said output terminals and said reference voltage, switching mean-s coupled to said regulating mean-s for disabling the same to protect said regulating means from the harmful effects of short circuits occurring in the load, said switching means including a transistor having base and emitter electrodes, and first and second bias elements serially connected between said base and emitter electrodes, said first element being coupled to said output terminals and responsive to the output voltage to provide a first voltage thereacross which varies directly with the output voltage and which drops substantially in response to a short circuit in the load, said second element being responsive to the current applied to the load and providing a second voltage thereacross which increases substantially in response to a short circuit in the load, said first and second voltages being of opposite polarity and adding in ing and changing when said first voltage drops and said second voltage increases in response to a short circuit in the load to cause said transistor to conduct so that said switching means disables said regulating means.

4. A voltage regulator including in combination, direct current potential supply means, output terminals for connection to a load, a control transistor connected to said supply means and to said output terminals, a Zener diode for supplying a reference voltage, circuit means including said control transistor and said Zener diode operating to apply current to one of said output terminals tending substantially to eliminate changes in voltage across the load in response to a detected difference between the voltage at said output terminals and the reference voltage across said Zener diode, a switching circuit for disabling said control transistor including a switching transistor having base, emitter and collector electrodes, said collector electrode being coupled to said control transistor, and first and second serially connected resistors connected between said base and emitter electrodes, said first resistor being coupled to said output terminals and switching transistor, said first and second voltage components balancing out changes resulting from simultaneous increase of output voltage and output current to provide a normal bias voltage holding said switching transistor non-conducting, said first and second voltages varying in opposite senses'in response to simultaneous decrease in output voltage and increase in output current to produce a bias voltage which renders said switching transistor conducting an d thereby disables said control transistor.

5. A voltage regulator system including in combination, direct current potential supply means, output terminals for connection to a load, regulating means connected between said supply means and said output terminals for holding the voltage at said output terminals at a predetermined value, and protection means including switch means coupled to said regulating means and operative to disable the same when a short circuit condition occurs in the load, said protecting means including first means coupled across said output terminals for producing a first voltage varying with the output voltage and which drops when a short circuit condition occurs in the load,

second means coupled in series with the output applied to the load and producing a second voltage of opposite polarity to said first voltage, said second voltage varying with the output current and increasing when a short circuit condition occurs in the load, means coupling said first and second means in series to said switch means for providing a bias voltage thereto resulting from the differential action of said first and second opposite polarity voltages, said switch means operating to disable said regulating means in response to the bias voltage resulting from the drop in said first voltage and the increase in said second opposite polarity voltage produced by a short circuit condition in the load.

References Cited in the file of this patent UNITED STATES PATENTS 2,697,811 Deming Dec. 21, 1954 2,832,900 Ford Apr. 29, 1958 2,888,633 Carter May 26, 1959 2,896,151 Zelinka July 21, 1959 2,904,742 Chase Sept. 15, 1959 2,922,945 Norris Ian. 26, 1960 2,994,029 Bixby July 25, 1961 

1. A DIRECT CURRENT VOLTAGE REGULATOR INCLUDING IN COMBINATION, INPUT SUPPLY TERMINALS, OUTPUT TERMINALS FOR CONNECTION TO A LOAD, A CONTROL TRANSISTOR CONNECTED BETWEEN SAID INPUT AND SAID OUTPUT TERMINALS, A ZENER DIODE FOR SUPPLYING A REFERENCE VOLTAGE, SAID CONTROL TRANSISTOR BEING COUPLED TO SAID ZENER DIODE AND OPERATIVE TO APPLY CURRENT TO ONE OF SAID OUTPUT TERMINALS SUBSTANTIALLY TO ELIMINATE CHANGES IN VOLTAGE ACROSS THE LOAD IN RESPONSE TO A DETECT DIFFERENCE BETWEEN THE OUTPUT VOLTAGE AND THE REFERENCE VOLTAGE SUPPLIED BY THE VOLTAGE DROP ACROSS SAID ZENER DIODE, A SWITCHING TRANSISTOR HAVING BASE, EMITTER AND COLLECTOR ELECTRODES, SAID COLLECTOR ELECTRODE BEING COUPLED TO ONE SIDE OF SAID ZENER DIODE, AND FIRST AND SECOND RESISTORS CONNECTED IN SERIES BETWEEN SAID BASE AND EMITTER ELECTRODES OF SAID SWITCHING TRANSISTOR AND PRODUCING A RESULTANT VOLTAGE TO NORMALLY BIAS OFF SAID SWITCHING TRANSISTOR, SAID FIRST RESISTOR BEING COUPLED ACROSS SAID OUTPUT TERMINALS AND HAVING A FIRST VOLTAGE DEVELOPED THEREACROSS WHICH VARIES DIRECTLY WITH THE OUTPUT VOLTAGE, SAID SECOND RESISTOR BEING COUPLED TO ONE OF SAID OUTPUT TERMINALS AND HAVING A SECOND VOLTAGE DEVELOPED THEREACROSS WHICH VARIES DIRECTLY WITH THE OUTPUT CURRENT APPLIED TO THE LOAD, SAID SECOND VOLTAGE BEING OF OPPOSITE POLARITY TO SAID FIRST VOLTAGE AND EXCEEDING SAID FIRST VOLTAGE UPONTHE OCCURRENCE OF A SIMULTANEOUS DECREASE IN OUTPUT VOLTAGE AND INCREASE IN OUTPUT CURRENT TO PROVIDE A RESULTANT BIAS VOLTAGE WHICH RENDERS SAID SWITCHING TRANSISTOR CONDUCTING, SAID SWITCHING TRANSISTOR REDUCING THE VOLTAGE ACROSS SAID ZENER DIODE TO CUT OFF SAID CONTROL TRANSISTOR. 